Data Sheet

LT4423

analog.com

Rev. 0

8 of 18

BLOCK DIAGRAM

THEORY OF OPERATION

The LT4423 is a single positive voltage ideal diode, utilizing two integrated back-to-back P-channel power MOSFETs

with a RON of 200mΩ. The IN pins form the anode, while the OUT pins form the cathode and are typically connected

in parallel with other diode cathodes in an ORing configuration.

By applying an input power supply to IN, between 1.9V and 28V, a load can be powered at OUT. An internal gate drive

amplifier (see Block Diagram) attempts to regulate the forward (IN - OUT) voltage drop to 15mV. The MOSFET gate

overdrive voltage adjusts to maintain the 15mV drop. At load currents above approximately 75mA, the internal

MOSFETs are fully on, and the forward voltage drop is governed by the ohmic relationship of ILOAD⠂RON.

Typical on-resistance (200mΩ) is achieved when IN ≥ 4V. Below IN = 4V, diminishing gate drive causes RON to increase,

as shown in the Typical Performance Curves. Operating with high RON and high currents will cause large forward

drops and temperature rise.

If the OUT voltage exceeds the IN voltage by approximately 20mV, the internal power MOSFET turns off quickly

through a fast comparator, disabling the power path. Once disabled, OUT is disconnected from IN.

The LT4423 is placed in shutdown mode by driving SHDN low. In shutdown, the device consumes very little

quiescent current (typically less than 500nA), the power path disables, and OUT is disconnected from IN. Driving

SHDN

high enables the power path, connecting the load at OUT to the input power supply connected to IN.

Integrated thermal protection disconnects the power path when the junction temperature exceeds 160°C (typical).

While the power path is disabled due to the overtemperature condition, the device remains active and consumes

power. Once the device cools down to about 145°C, the power path is restored (assuming the OUT voltage does not

exceed the IN voltage by approximately 20mV, and the device has not been placed into shutdown mode by driving

SHDN

low).

GND

IN

OUT

SHDN

STATUS

(OUT > IN)

INTERNAL

BIAS

THERMAL

SHUTDOWN

15mV

REGULATOR

15mV

UVLO

VMAX